Insert-molding method and and device therefor

ABSTRACT

The present invention relates to a method of producing an insert-molding product in which an insert product  2  is covered with a synthetic resin by arranging the insert product  2  in a cavity  11  of a mold  10,  holding the insert product by a holding pin  12,  pouring a molten synthetic resin  3  into the cavity  11,  and retracting the holding pin  12.  The moving pin  13  is provided adjacent to the holding pin  12.  After the cavity  11  is filled with the synthetic resin  3,  the holding pin  12  is retracted and the moving pin  13  is moved in the direction of the cavity  11  to extrude and introduce the synthetic resin  3  into the space where the holding pin  12  used to be positioned.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an insert-molding method forobtaining resin-molded products in which insert products such aselectronic parts are sealed with a resin to a sufficient degree withoutdeviation in position, and to a molding device therefor.

[0003] 2. Description of the Related Art

[0004] In order to maintain the water-proof properties of electronicparts, there have heretofore been employed a method by which thesurfaces of the electronic parts are covered with a potting material, amethod by which a resin sealing plug is attached thereto, and the likemethod.

[0005] In recent years, however, there has been widely employed a methodby which the surfaces are sealed with a resin in order to decrease thecost of products and to enhance the ratio of recycling. The sealing withthe resin is generally based on an insert-molding method which featuresexcellent mass-productivity at a decreased cost.

[0006] As the device used for the insert molding, there has heretoforebeen known the one disclosed in, for example, Japanese Unexamined PatentPublication (Kokai) No. 55-91642. That is, as shown in FIG. 10, therehas been proposed a molding device 9 comprising a mold 90 having acavity 91 in which will be arranged an insert product 2, and a holdingpin 92 retractably provided in the mold 90 to hold the insert product 2at a tip 921. Reference numeral 95 denotes a port for pouring-in thesynthetic resin.

[0007] Described below is an insert-molding method using theabove-mentioned mold 9.

[0008] First, the insert product 2 is arranged at a predeterminedposition in the cavity 91 being held by the holding pin 92. Next, thecavity 91 is filled with a synthetic resin 3 and, then, the holding pin92 is retracted from the cavity 91. Thereafter, the cavity is furtherfilled with the synthetic resin 3.

[0009] Thus, there is obtained a resin-molded product in which the wholesurface of the insertion product is sealed with the resin.

[0010] According to the above-mentioned insert-molding method anddevice, however, the quality of the molded product is affected by thetiming of retracting the holding pin 92 from the cavity 91. That is,when the holding pin 92 is retracted before the cavity 91 is completelyfilled with the synthetic resin 3, there remains no melted portioncaused by the holding pin 92, and the sealing with resin is accomplishedto a sufficient degree. Due to the synthetic resin 3 that is filled,however, the insert product 2 moves and its position is deviated. Whenthe holding pin 92 is retracted after the cavity 91 is completely filledwith the synthetic resin 3, on the other hand, the space in which theholding pin 92 used to be positioned is not sufficiently filled with thesynthetic resin 3, and the insert product 2 is not sealed with the resinto a sufficient degree.

[0011] There has further been proposed a method according to which thesynthetic resin 3 is forcibly extruded and introduced into space wherethe holding pin used to be positioned as disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 57-163528 or JapaneseUnexamined Patent Publication (Kokai) No. 8-306718.

[0012] That is, as shown in FIG. 11, a device 8 used for this methodincludes a mold 80 having a cavity 81, a cylindrical holding pin 82retractably provided in the mold 80, and a pole-like moving pin 83retractably provided in the holding pin 82.

[0013] Briefly described below is the insert-molding method by using theabove-mentioned molding device 8.

[0014] That is, referring to FIG. 11, an insert product 20 is arrangedin the cavity 81 and is held by the holding pin 82. The cavity 81 isthen filled with the synthetic resin 3.

[0015] Then, as shown in FIG. 12, the moving pin 83 is moved in thedirection of the cavity 81 while the holding pin 82 is retracted, andthe synthetic resin 3 is forcibly extruded and introduced into spacewhere the holding pin 82 used to be positioned.

[0016] The insert product 20 has a through hole 201 formed in thecentral portion thereof and an accessory 202 such as a reed frame on theend surfaces thereof, the accessory 202 extending beyond the cavity 81so as to be held by the mold 80.

[0017] However, the above-mentioned conventional insert-molding methodand device have problems as described below.

[0018] That is, after the synthetic resin 3 is introduced, the surfaceof the synthetic resin 3 contacting to the holding pin 82 is cooled bythe holding pin 82, resulting in the formation of a skin layer(solidified layer on the surface of the resin) 31.

[0019] The holding pin 82 has a cylindrical shape and, hence, the skinlayer 31 assumes a cylindrical shape, too, as shown in FIG. 13.

[0020] Therefore, the area of the skin layer 31 inevitably increases butis never concentrated to one point despite being extruded by the movingpin 83.

[0021] Accordingly, the skin layer 31 does not melt again despite of theambient heat or pressure, and the unmelted portion is very likely toremain.

[0022] When the holding pin 82 is retracted at a delayed timing,therefore, the unmelted portion remains and the insert product 20 is notsealed with the resin to a sufficient degree.

SUMMARY OF THE INVENTION

[0023] The present invention was accomplished in view of theabove-mentioned problem inherent in the prior art, and its object is toprovide an insert-molding method capable of sealing an insert productwith a resin to a sufficient degree without permitting the position ofthe insert-product to be deviated as a result of suppressing theresidence of the unmelted portion caused by the holding pin, and amolding device therefor.

[0024] A first aspect of the present invention is concerned with aninsert-molding method in which an insert product is arranged in a cavityof a mold and is held by a holding pin, a molten synthetic resin ispoured into said cavity, and said holding pin is retracted to obtain aninsert-molding product in which said insert product is covered with saidsynthetic resin, wherein a moving pin is provided adjacent to saidholding pin, said moving pin is moved in the direction of the cavitywhile retracting said holding pin after said cavity is filled with saidsynthetic resin, and said synthetic resin is extruded and introducedinto space where said holding pin used to be positioned.

[0025] In the present invention, what most draws attention is that themoving pin is moved in the direction of the cavity while retracting theholding pin after the cavity is filled with the synthetic resin, and thesynthetic resin is extruded and introduced into space where the holdingpin used to be positioned.

[0026] A second aspect of the present invention is concerned with amolding device for carrying out the above-mentioned molding method toproduce an insert-molding product in which an insert product is coveredwith a synthetic resin, comprising a mold having a cavity for molding,and a holding pin retractably provided in said mold to hold the insertproduct, wherein said mold has a moving pin that retractably moves inthe direction of the cavity adjacent to said holding pin.

[0027] In this molding device, what most draws attention is that themoving pin retractably moves in the direction of the cavity adjacent tothe holding pin.

[0028] Therefore, the molding device of the invention makes it possibleto produce an insert-molding product in which the insert product issealed with the resin to a sufficient degree while suppressing thedeviation in position of the insert product.

[0029] The present invention may be more fully understood from thedescription of preferred embodiments of the invention set forth belowtogether with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a sectional view of an insert-molding device accordingto an embodiment 1 of the present invention;

[0031]FIG. 2 is a view illustrating a state of just before a holding pinis retracted in an insert-molding method according to the embodiment 1of the present invention;

[0032]FIG. 3 is a view illustrating a state of just after the holdingpin is retracted in the insert-molding method according to theembodiment 1 of the present invention;

[0033]FIG. 4 is a view illustrating a state of after the moving pin ismoved in the insert-molding method according to the embodiment 1 of thepresent invention;

[0034]FIG. 5 is a perspective view of an insert-molding product obtainedby the insert-molding method according to the embodiment 1 of thepresent invention;

[0035]FIG. 6 is a sectional view of an insert-molding device accordingto an embodiment 2 of the present invention;

[0036]FIG. 7 is a sectional view of the insert-molding device accordingto an embodiment 3 of the present invention;

[0037]FIG. 8 is a sectional view illustrating the periphery of theholding pin in the insert-molding device according to an embodiment 4 ofthe present invention;

[0038]FIG. 9 is a diagram illustrating the measured results of changesin the temperature of the synthetic resin near the holding pin accordingto experiment of the present invention;

[0039]FIG. 10 is a sectional view of a conventional insert-moldingdevice;

[0040]FIG. 11 is a sectional view of another conventional insert-moldingdevice;

[0041]FIG. 12 is a sectional view illustrating a state of after theholding pin is retracted and the moving pin is moved in the anotherconventional insert-molding device; and

[0042]FIG. 13 is a sectional view along the line C-C in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The insert-molding method and device according to an embodiment 1of the present invention will now be described with reference to FIGS. 1to 5.

[0044] Referring to FIG. 1, an insert-molding device 1 of thisembodiment possesses a mold 10 having a cavity 11 for molding, and aholding pin 12 retractably provided in the mold 10 to hold an insertproduct.

[0045] The insert-molding device 1 is the one for producing aninsert-molding product 4 (FIG. 5) in which the insert product 2 iscovered with a synthetic resin 3.

[0046] The mold 10 has a moving pin 13 that retractably moves in thedirection of the cavity 11 adjacent to the holding pin 12.

[0047] The moving pin 13 is arranged to surround the holding pin 12 inconcentric therewith.

[0048] The mold 10 has a guide hole 14 for guiding the moving pin 13 inthe direction of the cavity 11.

[0049] In this embodiment, the holding pin 12 has a diameter of 3.0 mm.

[0050] In FIG. 1, furthermore, reference numeral 15 denotes a port forpouring the synthetic resin 3.

[0051] The insert product 2 is a speed sensor used for measuring thespeed of an automobile or the like, and comprises a sensor terminal 21,a coil 22, a primary spool 23 and a magnet 24. The insert product 2further has a lead wire 25 which, during the insert-molding, extends outof the mold 10 through a cable tube 26 that covers the lead wire 25.

[0052] A holding dent 28 with which an end of the holding pin 12 willcome in contact is formed in the upper end of the insert product 2.

[0053] The molding method using the above-mentioned insert-moldingdevice 1 will now be described.

[0054] Referring to FIG. 1, first, the insert product 2 is arranged inthe cavity 11 of the mold 10, and the holding dent 28 at the upper endof the insert product 2 is held by an end 128 of the holding pin 12.

[0055] Then, the synthetic resin 3 in a melted state is poured into thecavity 11. At this moment, the end 138 of the moving pin 13 ispositioned on the inside of an open end 141 of the guide hole 14.

[0056] Referring next to FIG. 2, the cavity 11 is filled with thesynthetic resin 3 and, then, the holding pin 12 is retracted (FIG. 3)and, at the same time, the moving pin 13 is moved in the direction ofthe cavity 11 until the end 138 thereof is located at the same positionas the open end 141 (FIG. 4). Therefore, the synthetic resin 3 filled inthe guide hole 14 is extruded into the cavity 11.

[0057] Accordingly, the synthetic resin 3 is extruded and introducedinto space 32 (see FIG. 2) in which the holding pin 12 used to bepositioned.

[0058] Through the series of steps described above, there is produced aninsert-molding product 4 (see FIG. 5) in which the insert product iscovered with the synthetic resin 3.

[0059] In FIG. 5, reference numeral 41 denotes a mark of the holding pinformed like a dent by the end 128 of the holding pin 12.

[0060] Next, described below are the action and effect of thisembodiment.

[0061] Referring to FIG. 2, when the holding pin 12 is retracted afterthe cavity 11 is filled with the synthetic resin 3, space is once formedin a portion where the holding pin 12 used to be positioned. The space32 is then filled with the surrounding synthetic resin 3 but not to asufficient degree (FIG. 3). Upon moving the moving pin 13 adjacent tothe holding pin 12 as shown in FIG. 4, however, the synthetic resin 3surrounding the space 32 is extruded and introduced into the space 32.Thus, the space disappears.

[0062] Furthermore, a skin layer (solidified layer on the surface of theresin) is formed on the surface of the synthetic resin 3 contacting theholding pin 12. Due to the pressure of the surrounding synthetic resin3, however, the skin layer is concentrated to one point and melts againdue to the pressure and heat of the synthetic resin 3.

[0063] In this embodiment, in particular, since only one holding pin 12is used, the skin layer is not formed at all.

[0064] Accordingly, the insert product can be sealed with the resin to asufficient degree.

[0065] The holding pin 12 is retracted after the synthetic resin 3 hasbeen introduced and, hence, the position of the insert product 2 is verylittle deviated.

[0066] According to this embodiment, therefore, it is possible toproduce the insert-molding product in which the insert product is sealedwith the resin to a sufficient degree without causing the position ofthe insert product to be deviated.

[0067] In the present invention, it is desired that one holding pin 12is employed. In this case, the unmelted portion can be completelyextinguished.

[0068] It is further desired that the holding pin 12 has a diameter offrom 1.0 mm to 6.0 mm. When the diameter is smaller than 1.0 mm, itbecomes difficult to hold the insert-molding product. When the diameterexceeds 6.0 mm, on the other hand, it is likely that the unmeltedportion is formed to some extent.

[0069] It is desired that the moving pin 13 is arranged to surround theholding pin 12 in concentric therewith.

[0070] In this case, the synthetic resin can be extruded and introducedinto the space where the holding pin 12 used to be positioned from thewhole circumference thereof and uniformly. Therefore, the syntheticresin can be efficiently and reliably extruded and introduced into thespace.

[0071] It is therefore allowed to more reliably produce theinsert-molding product in which the insert product is sealed with theresin.

[0072] In embodiment 2, as shown in FIG. 6, the moving pin 13 isarranged separately from, and in parallel with, the holding pin 12.

[0073] In other respects, embodiment 2 is the same as embodiment 1.

[0074] In this case, the insert-molding device 1 can be constructedrelatively simply. In other respects, embodiment 2 exhibits the sameaction and effect as embodiment 1.

[0075] In embodiment 3, as shown in FIG. 7, the moving pin 13 isarranged at right angles with the holding pin 12. In other respects,embodiment 3 is the same as embodiment 1.

[0076] In this case, a plunger for moving the moving pin 13 back andforth, and a cylinder for moving the holding pin 12 back and forth, canbe arranged at separate places unlike that of embodiment 1. Therefore,their arrangement is facilitated.

[0077] In other respects, the action and effect are the same as those ofembodiment 1.

[0078] In embodiment 4, as shown in FIG. 8, a cylindrical recessedportion is formed in the holding pin 12, and a spiral heater 121 iscontained therein.

[0079] In other respects, embodiment 4 is the same as embodiment 1.

[0080] When the cavity 11 is filled with the synthetic resin 3 in thiscase, no skin layer is formed on the surface of the synthetic resin 3surrounding the holding pin 12 and contacting holding pin 12.

[0081] This is because the synthetic resin 3 surrounding the holding pin12 is maintained at a high temperature owing to the heater 121 containedin the holding pin 12. Therefore, the synthetic resin 3 is notsolidified.

[0082] Therefore, this embodiment makes it possible to produce aninsert-molding product in which the insert product is sealed with theresin more reliably.

[0083] In the present invention, it is desired that the metal mold 10has a guide hole 14 for guiding the moving pin 13 in the direction ofthe cavity, the end of the moving pin 13 is located on the inside of theopen end of the guide hole 14 when the cavity is to be filled with thesynthetic resin, the holding pin 12 is retracted after the cavity 11 isfilled with the synthetic resin, and the moving pin 13 is moved in thedirection of the cavity 11.

[0084] When the cavity 11 is filled with the synthetic resin in thiscase, the guide hole 14, too, is filled with the synthetic resin up tothe end of the moving pin 13.

[0085] Therefore, the moving pin 13 is moved in the direction of thecavity while the holding pin 12 is being retracted, and the syntheticresin filled in the guide hole 14 is extruded into the cavity 11.Accordingly, the synthetic resin is extruded and introduced into thespace where the holding pin 12 used to be positioned.

[0086] That is, according to the present invention, the synthetic resinto be introduced into the space in the guide hole 14 and can, hence, beextruded and introduced into the space to a sufficient degree.

[0087] It is therefore possible to produce the insert-molding product inwhich the insert product is sealed with the resin more reliably.

[0088] In an experimental example of the present invention as shown inFIG. 9, a change in the temperature of the synthetic resin near theholding pin 12 was measured when the holding pin 12 was retracted inconducting the insert-molding according to the present invention.

[0089] The measurement was taken while conducting the insert-moldingshown in embodiment 1 by installing the temperature sensors at a point Aand a point B shown in FIG. 3.

[0090] The point A is near the open end 141 of the guide hole 14 of themold 10, and the point B is almost midway between the open end 141 andthe holding dent 21 at the upper end of the insert product 2.

[0091] During the insert-molding, the measurement was started from amoment when the holding pin 12 was retracted. Thereafter, changes in thetemperature of the synthetic resin 3 were monitored at the points A andB.

[0092] The results of measurement are as shown in FIG. 9.

[0093] As will be seen from FIG. 9, the temperature of the syntheticresin 3 at the point A sharply drops after the cavity 11 is filled withthe synthetic resin, remains stable at about 100° C., and does not risethereafter. At the point B, the temperature of the synthetic resin 3once drops but rises again after the holding pin 12 is retracted. Thetemperature exceeds 230° C. which is the melting point of the syntheticresin for about one second from about 0.7 seconds after the retractionof the holding pin 12 until about 1.7 seconds after.

[0094] That is, during the above-mentioned period of one second, theskin layer melts and adheres again due to the pressure and heat of thesurrounding synthetic resin 3.

[0095] It will thus be understood that the insert product 2 is sealedwith the resin to a sufficient degree upon moving the moving pin 13within about 1.7 seconds after the holding pin 12 is retracted.

[0096] While the invention has been described with reference to specificembodiments selected for purposes of explanation, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

1. An insert-molding method in which an insert product is arranged in acavity of a mold and held by at least one holding pin, a moltensynthetic resin is poured into said cavity, and said holding pin isretracted to obtain an insert-molding product which said insert productis covered with said synthetic resin, wherein said holding pin isretracted after said cavity is filled with said synthetic resin which isextruded and introduced into space where said holding pin was located.2. An insert-molding method according to claim 1, wherein at least onemoving pin is placed adjacent to said holding pin, and said moving pinis moved in the direction of the cavity to extrude and fill saidsynthetic resin into the space where said holding pin used to belocated.
 3. An insert-molding method according to claim 2, wherein saidmoving pin is arranged to surround said holding pin and to be concentrictherewith.
 4. An insert-molding method according to claim 2, whereinsaid moving pin is arranged parallel with said holding pin.
 5. Aninsert-molding method according to claim 2, wherein said moving pin isarranged at right angles with said holding pin.
 6. An insert-moldingmethod according to claim 2, wherein said holding pin contains a heater.7. An insert-molding method according to claim 2, wherein said mold hasa guide hole for guiding said moving pin in the direction of the cavity,an end of said moving pin is located on the inside of an open end ofsaid guide hole when said cavity is being filled with said syntheticresin, and after said cavity is filled with said synthetic resin, saidmoving pin is moved in the direction of the cavity while retracting saidholding pin.
 8. A molding device, for producing an insert-moldingproduct in which an insert product is covered with a synthetic resin,comprising a mold having a cavity for molding, and a holding pinretractably provided in said mold to hold the insert product, whereinsaid mold has a moving pin that retractably moves in the direction ofthe cavity adjacent to said holding pin.
 9. A molding device accordingto claim 8, wherein said moving pin is arranged to surround said holdingpin and to be concentric therewith.
 10. A molding device according toclaim 8, wherein said moving pin is arranged parallel with said holdingpin.
 11. A molding device according to claim 8, wherein said moving pinis arranged at right angles with said holding pin.
 12. A molding deviceaccording to claim 8, wherein said holding pin contains a heater.
 13. Amolding device according to claim 8, wherein said mold has a guide holefor guiding said moving pin in the direction of the cavity.